Scientists say it might one day be possible to end the need for blood donation by creating supplies from human stem cells.

A University of Minnesota team transformed stem cells taken from discarded IVF embryos into immature blood cells.

UK experts have warned the technology is at an early stage, and may never provide an alternative to donation.

The findings are published in the journal Experimental Hematology.

I suspect blood donation will remain the much quicker and easier alternative.

Professor Chris Higgins

Stem cells are the body's master cells, with the ability to transform into any type of tissue.

The Minnesota team were able to use different combinations of chemicals called growth factors, which occur naturally in the body, to turn embryonic stem cells into cells which showed the characteristics of various types of adult blood cell.

Not only do they believe blood created in this way would be free of the diseases which can sometimes contaminate donor blood supplies, they are also confident that it would pose no problems of rejection when given to patients.

Lead researcher Dr Dan Kaufman said: "These findings do more than give us a basic understanding of blood cell replacement - they allow us to consider potential future therapies.

"We can envision blood therapies completely compatible with the patient, such as use of embryonic stem cells to make red blood cells for platelets used in blood transfusions, or a source of new blood supply free of any viruses.

"They might also be a source for bone marrow transplants, especially for those patients who do not otherwise have an appropriately matched donor."

Significance questioned

However, Professor Chris Higgins, director of the Medical Research Council Clinical Sciences Centre at Hammersmith Hospital, London, told the BBC News website other groups had carried out similar work.

He said: "This seems only to be an incremental step forward, and whether it is going to be clinically useful or not is very speculative.

"I suspect blood donation will remain the much quicker and easier alternative."

A spokesperson for the National Blood Service said the research was still at an early stage.

However, she added: "The NBS welcomes developments that may result in even safer treatments for patients."